The disclosure relates to connector part comprising a body part for connecting to a counterpart for creating a fluid tight seal when fitted together. The disclosure relates further to fluid connection structure using the connector part.
As described above the disclosure relates generally to a fluid connection for reducing a fluid volume and making a secure seal in said connection. Especially the disclosure describes the fluid connection to reduce an extra fluid volume when using connectors made using multi shot injection molded parts. The disclosure relates also to sample tubing connections used in analyzing equipment such as gas analyzing equipment for patient respiratory gas.
In anesthesia or in intensive care, the condition of a patient is often monitored e.g. by analyzing the air exhaled by the patient for its carbon dioxide content. For this reason a small portion of the respiratory gas is delivered to a gas analyzer. The sample is carried along a sampling tube connected in one end often to a respiratory tube adapter and the other end to the gas analyzer. This sampling tube is typically disposable and must have some kind of reliable and tight but simple and cheap connectors.
Almost all pneumatic connectors in the respiratory system used earlier in the field have tapered conical contact surfaces. Such connectors are simple, easy to connect and cheap to make and they still provide an airtight and reliable connection. The connection such as a well-known fitting called Luer-Lok, a registered trademark of Becton Dickinson of Franklin Lakes, N.J. USA, has been in general use for gas sampling but also other similar connectors with differing dimensions can be used.
The tapered portion of the connector is normally conical with straight cross section sides because it gives a reliable and tight connection using a large contact area. The tapered portion could in principle also have curved cross section sides or one tapered connector in combination with a suitably designed semi-rigid counterpart. The contact surface responsible for the tightness is always on the tapered portion of the connector.
A gas analyzer designed to measure respiratory gas in real time has to be fast enough to resolve changes in the gas content. This is especially true for carbon dioxide, which varies from close to zero in the inspiratory phase to about 5% in the expiratory phase of the breathing cycle. It is then very important to streamline the complete gas sampling system. Many portions of the system with slowed down response can easily add up to unacceptable performance of the gas analyzer.
The reason for an increased rise time of e.g. carbon dioxide is often an extra fluid volume, a dead space in the pneumatic line, where the gas flow is slowed down. The tapered conical connector is susceptible to such dead space, especially if the inner dimensions are significantly larger than those of the bore or sampling line itself. The inherent construction of the conical connector is such that dead space always is introduced and the amount is critically dependent on the tolerance of the conical dimensions. The connectors must allow for axial or longitudinal play in order to avoid the situation of touching axially because then air leak is likely to occur. Therefore, the tolerances always define an axial extra fluid volume in the connection to ensure tightness at the conical surfaces.
Minimal dead space is essential also in gas or liquid chromatography. An attempt to make connections with capillaries is described for example in U.S. Pat. No. 6,969,095 B2. The female part of the connection is slightly tapered in order to accept the cylindrical capillary tube and make a tight press-fit. This connector fitting is specially designed for conditions encountered in liquid or gas chromatography and is not intended for repeatedly made reliable connections like in gas analyzers. Robustness inevitably adds dead space to the bore of the connection.
In neonatal main ventilation circuits, extra fluid volume has to be as small as possible. There are different solutions to this problem. The connections are also conically tapered even if the dimensions are much larger than what would be used for a gas sampling system. In one solution there is a sliding internal passage filling the dead space and in another solution a compressible member is used to exclude the extra fluid volume.
With the current Luer-Lok type design it is impossible to know if the connector is connected leak-proof. The connectors can wedge together so that the connection seems to be tight but it is in fact leaking. Gas sampling done by suction created by a pump can dilute if there is a leak in the sampling line. Ventilator pressure changes will also influence the gas sampling if there is a leak in the sampling line.